PREV DISCUSSION
/Issued 854 AM PDT Fri Jul 5 2024/

DISCUSSION...Clear skies continue today, and this will aid the return of dangerous heat this afternoon along with ridging. West side valleys are still on track to see triple digit highs this afternoon. The heat products (Excessive Heat Warnings west of the Cascades and Heat Advisories east) continue through Monday. The day will be spent reviewing the heat into early next week as these products may need to be extended.

A Red Flag Warning will be in effect from 4 PM to 8 PM this afternoon for strong, gusty winds and low relative humidities. This will be in effect in the Rogue Valley and southern Umpqua Basin into Roseburg. Please review the previous forecast discussion for further forecast information. -Hermansen

MARINE
Updated 815 AM Friday, July 5, 2024
Northerly winds under a persisting thermal trough continue to bring wind-driven steep seas to all waters. While seas are just at Advisory thresholds, the wide area and duration of the continuing hazard supports a Small Craft Advisory through Saturday at 11 PM. Some local areas of Advisory-level seas may continue at 40-60 nm from shore past this time and will continue to decrease into early Sunday morning.

The brief period of sub-Advisory seas ends Monday morning as a thermal trough rebuilds in waters south of Cape Blanco. The wind- built waves look to remain at small craft levels with possibly small areas of very steep and hazardous seas south of Brookings Monday night. Long-term probabilistic guidance currently shows a 50-70% chance for waves over 12 feet by Thursday as well as as a 25% chance for areas of gale force gusts south of Gold Beach on Thursday evening. The confidence is not nearly approaching high enough to make a forecast for conditions nearly a week out, but at the very least active seas do look to return and remain for much of next week. -TAD/Hermansen

PREV DISCUSSION... /Issued 446 AM PDT Fri Jul 5 2024/

Updated AVIATION discussion

DISCUSSION...After due consideration, have continued with the inherited set of hazards. After one more new set of data, expect the day shift to prominently consider whether to extend the Excessive Heat Warning and Heat Advisory (now in effect through Monday evening) for another 24 hours into Tuesday, and whether to upgrade the Fire Weather Watches currently in effect for Saturday afternoon through Sunday evening. The higher probability is for the latter, with a majority of models indicating a slight strengthening trend for afternoon winds from today through Sunday, while the peak of the heat wave still looks to occur on Saturday, then nearly as hot on Sunday.

Three max temperature records were broken Thursday. The broken records were 105 at Medford, 98 at Mt. Shasta City, and 104 at Montague. More records are expected to be broken as the heat wave continues into next week. Though Brookings very likely saw their peak of the heat a couple of days ago, at 98 on Wednesday, a weaker northeast flow will continue much above normal high temperatures through at least Saturday, and possibly through Monday.

Besides the heat, low humidity, and gusty winds, the natural concern is to be vigilant for any risk of thunderstorms. At this time, that risk looks extremely small with weak instability, but especially due to a lack of mid-level 700-500mb moisture available in the region, perhaps a modest uptick of moisture on the east side by Wednesday afternoon. There is also a contingent of ensemble members indicating some instability and increase of available moisture on the east side with a shift to a southwesterly flow aloft late next week around Day 7/Friday and/or Day 8/Saturday.

FIRE WEATHER
Issued 230 AM Friday July 5, 2024
Heatwave underway and main concern for this period is weather contribution to fire danger through the weekend. Initially the combination of wind and low humidity is a concern for the west side as forecasts humidities range from the upper single digits to low teens and winds range from sustained 6-12 mph. Prime area of concern for Friday afternoon and evening is the low elevation I-5 corridor from Roseburg to Grants Pass, Medford, and Ashland.

More of the similar condition will then occur with slightly hotter, slightly drier, and slightly stronger winds expected Saturday across a broader area. In addition to the abnormally hot and dry weather being realized in our local forecast grids, the HDW (Hot Dry Windy) index online is showing the condition as advertised by the GEFS members to fall within the top 5% of these events over the 30-year climatology from 1981-2010. In short, this is very unusual to have the area this hot, dry and (breezy)
for this time of year. So, this occurring across the holiday weekend was the final consideration. Despite no lightning, there will be other potential sources of ignition.

The heat will continue into the early part of next week. Compared to Saturday, this includes what looks to be a further very slight strengthening of afternoon winds on Sunday with conditions almost as hot and dry. During Monday, a short wave trough is advertised to come up the northern California coast which is a pattern often supportive of thunderstorms. But, not seeing the moisture to get us worried at this point, but also the solutions are deviating from one another quite a bit so confidence in strength, track and timing of the low is...low. Keep an ear out on this development. -Stavish/DW

MFR WATCHES/WARNINGS/ADVISORIES
OR...Excessive Heat Warning until 9 PM PDT Monday for ORZ023>026.

Red Flag Warning from 4 PM this afternoon to 8 PM PDT this evening for ORZ616-620>623.

Fire Weather Watch from Saturday afternoon through Sunday evening for ORZ616-617-620>624.

Heat Advisory until 9 PM PDT Monday for ORZ029>031.

CA...Excessive Heat Warning until 9 PM PDT Monday for CAZ080>082.

Fire Weather Watch from Saturday afternoon through Sunday evening for CAZ280-284.

Heat Advisory until 9 PM PDT Monday for CAZ083>085.

PACIFIC COASTAL WATERS...Small Craft Advisory until 11 PM PDT Saturday for PZZ350-356-370-376.